1. Field of the Invention
The present invention relates to a construction machine such as a hydraulic shovel and the like.
2. Description of the Background Art
Regarding a conventional construction machine, its mainstream is a-hydraulically-operated system. For example, in a hydraulic shovel, driving of a farm working machinery, revolution of an upper revolving body, and traveling of a lower traveling body are performed by a hydraulic actuator (hydraulic cylinder, hydraulic motor). Operations are executed by controlling the pressure oil which is discharged from a hydraulic pump whose drive source is an engine and which is supplied to that hydraulic actuator.
Operations of the hydraulic shovel are not always operations which need 100% power with respect to the engine capacity but are operations which need for example only 90% or 80% power in many cases. That is, as shown in FIG. 8 which is an engine-torque characteristic view, set are operation modes such as a point PS of “regular load mode” in which a regular load operation is executed, a point PL of “light load mode” in which a light load operation is executed, and the like, with respect to a point PH of “heavy load mode” in which a heavy load operation of 100% power output is executed. An equal horsepower control (the discharge of the hydraulic pump is controlled according to PQ curves (iso-horsepower contours) so as to obtain a drive torque at a matching point) is performed so that the drive torques of the hydraulic pump at each points PH, PS, PL match the output torques of the engine, to make effective use of the engine output to improve fuel efficiency. Here, the drive torque of the hydraulic pump means the torque that the engine is required by the hydraulic pump in order to drive the hydraulic actuator.
In the hydraulic shovel, mounted is an engine having an output corresponding to a maximum required horsepower of when a vehicle operates, that is, an engine in which the rated output point PH of the engine torque curve corresponds to a point on a maximum required horsepower line L shown in FIG. 8. FIG. 9 shows a graph depicting changes of an absorption horsepower of the hydraulic pump in one cycle at the time of performing “digging and loading operation” in which dug earth and sand is rotated to be loaded on a truck body in the “regular load mode” in which matching occurs at 90% of the rated output of the engine. The load change of the hydraulic shovel is very large as compared to a passenger car and the like, and its engine has sufficient horsepower as shown in the graph, wherein the average load rate with respect to the maximum horsepower of the engine in one cycle is approximately 80%, and wherein the average load rate of the engine in the case where one day operation including traveling/moving, waiting for a truck vehicle, and the like, is measured is approximately 60%. Similarly, when operations in the “heavy load mode” are performed, the average load rate does not become 100% due to load changes. That is, in the hydraulic shovel in which an engine having an output corresponding to a maximum required horsepower is mounted, the output that the engine can output has not been employed effectively.
In order to solve such problem, conventionally, it has been proposed to employ a hybrid type construction machine provided with an engine, an electrical power generator driven by the engine, a battery to charge for electric power generated by the electrical power generator, and an electric motor driven by electrical power of the battery for example as shown in patent document 1. A hybrid type construction machine according to this patent document 1 will be explained below.
FIG. 10 shows a drive system block diagram of the hydraulic shovel that is the conventional hybrid type construction machine. In the drawing, the pressure oil which is discharged from a variable capacity type hydraulic pump 32 driven by an engine 31 is supplied to various actuators 44, 44 (for example, a boom cylinder 44a, an arm cylinder, a bucket cylinder, a travel motor, and the like) via a control valve 33. The speed of the engine 31 is controlled by a governor 31a which receives a governor command from a controller 35. A first electric motor 37 which is integral with a flywheel is attached to the engine 31, and the first electric motor 37 is connected to a battery 39 via a first inverter 38 and a controller 35. The first electric motor 37 has the function as an electrical generator also and is constructed in such a way that motor operation for assisting the hydraulic pump driving by the engine 31 and electrical power generation operation in which electrical power is generated using the engine 31 as a drive source can be operationally switched in response to the command from the controller 35. Operation signals from various operation levers 34, 34 and detection signals from various sensors 36, 36 (rotation sensor, pressure sensor, torque sensor, or the like) are input to the controller 35, and various kinds of control is performed based on these signals.
An upper revolving body 42 of the hydraulic shovel is rotatable by means of a second electric motor 40 via a speed reducer 43, and the second electric motor 40 is connected to the battery 39 via a second inverter 41 and the controller 35. The second electric motor 40 has the function as an electrical power generator also, similarly to the first electric motor 37 and is constructed in such a way that motor operation to drive the upper revolving body 42 and electrical power generation operation by inertial energy of the upper revolving body 42 of the time of restricting rotation can be operationally switched in response to the command from the controller 35.
A bypass conduit 46 having a hydraulic motor 47 is provided on a conduit 45 of the bottom side of the boom cylinder 44a, and the hydraulic motor 47 is driven when return oil from the boom cylinder 44a passes through the bypass conduit 46. An electrical power generator 48 is connected to the hydraulic motor 47 and to the battery 39 via an AC/DC converter 49.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-275945
In the hydraulic shovel, when an operational load is small and the drive torque of the hydraulic pump 32 is smaller than a predetermined output torque of the engine 31, the first electric motor 37 generates electricity by excess part of the engine output so that the battery 39 charges this generated electricity. When the operational load is large and the drive torque of the hydraulic pump 32 is larger than the predetermined output torque of the engine, the first electric motor 37 is driven by the electric power_stored in the battery 39 to assist the engine 31 to drive the hydraulic pump 32. Further, the hydraulic shovel is constructed in such a way that the electrical energy obtained when the second electric motor 40 is driven utilizing the inertial energy of the upper revolving body 42 at the time of revolution braking as well as the electrical energy obtained when the electrical power generator 48 is driven utilizing potential energy by high pressure return oil from the boom cylinder 44a are stored in the battery 39.
In such hydraulic shovel, excess energy of the engine 31 collected via the first electric motor 37, the inertial energy of the upper revolving body 42 collected via the second electric motor 40, and the potential energy of the boom cylinder 44a collected via the electrical power generator 48 are all converted into electrical energy. However, in attempting to reliably collect all energy described above and charge into the battery 39, there are problems that the respective electric motors 37, 40 and the electrical power generator 48 become large-sized and that a large capacity electricity storage device such as the battery 39 and the like becomes necessary.